Impaired Cerebral Autoregulation during Head Up Tilt in Patients with Severe Brain Injury

Abstract

Early mobilization is of importance for improving long-term outcome for patients after severe acquired brain injury. A limiting factor for early mobilization by head-up tilt is orthostatic intolerance. The purpose of the present study was to examine cerebral autoregulation in patients with severe acquired brain injury and a low level of consciousness. Fourteen patients with severe acquired brain injury and orthostatic intolerance and fifteen healthy volunteers were enrolled. Blood pressure was evaluated by pulse contour analysis, heart rate and RR-intervals were determined by electrocardiography, middle cerebral artery velocity was evaluated by transcranial Doppler, and near-infrared spectroscopy determined frontal lobe oxygenation in the supine position and during head-up tilt. Cerebral autoregulation was evaluated as the mean flow index calculated as the ratio between middle cerebral artery mean velocity and estimated cerebral perfusion pressure. Patients with acquired brain injury presented an increase in mean flow index during head-up tilt indicating impaired autoregulation (P < 0.001). Spectral analysis of heart rate variability in the frequency domain revealed lower magnitudes of ~0.1 Hz spectral power in patients compared to healthy controls suggesting baroreflex dysfunction. In conclusion, patients with severe acquired brain injury and orthostatic intolerance during head-up tilt have impaired cerebral autoregulation more than one month after brain injury.

Diffuse optical assessment of cerebral‐autoregulation in older adults stratified by cerebrovascular risk

“…The goal of the present study is to test whether LFO gains of cerebral hemodynamic variables, quantified by our innovative hybrid optical instrument, are useful biomarkers to distinguish two groups of cognitively healthy older subjects with high-or low-risk for developing CVD. Upon comparison with literature [21,26,[33][34][35][36][37][38][39], we believe this study is innovative in that: (a) it used an innovative hybrid optical instrument to simultaneously measure multiple cerebral hemodynamic parameters including rCBF, Δ[HbO 2 ] and Δ[Hb] in cerebral microvasculature. Multiple cerebral functional parameters provided more comprehensive assessment of brain activities than a single parameter alone, (b) it studied a unique population: cognitively healthy older subjects stratified by cerebrovascular risk and (c) it innovatively explored CAs (extracted from LFO gains of cerebral hemodynamics) as new biomarkers for diagnosis of CVD at preclinical stage.…”

“…TCD/NIRS has been used to measure LFOs in CBFV/ cerebral blood oxygenation for CA assessment [33][34][35][36]. Different orthostatic protocols were applied to induce MAP fluctuations for evaluating dynamic CA including a sit-stand maneuver [37] and tilting bed.…”

“…Different orthostatic protocols were applied to induce MAP fluctuations for evaluating dynamic CA including a sit-stand maneuver [37] and tilting bed. [33] The selected LFO frequency intervals varied in different studies [26,34,36,37], and study cohorts included age-matched older healthy subjects and patients with symptomatic carotid occlusion, ischemic stroke, or Alzheimer disease (AD) [21,35,38,39]. Previous studies have found that CAs (associated with LFO gains) were impaired in patients with symptomatic carotid occlusion or ischemic stroke [21,38,39], but preserved in patients with AD [35].…”

Statistical analysis plan for early mobilisation by head-up tilt with stepping versus standard care after severe traumatic brain injury – a randomised clinical feasibility trial

“…The data management plan and standard operating procedure are kept at the Copenhagen Trial Unit. * The standard deviation of the CRS-R was estimated from the change value of two studies and used to estimate the minimal relevant difference (SD/2) [23,24] ** The standard deviation of the EFA score was estimated from two observational studies investigating patients with brain injury approximately 1.5 months after injury and used to estimate the minimal relevant difference (SD/2) [25,26] *** The FIM standard deviation and minimal relevant difference has been investigated in two studies on patients with brain injury [16,17] Supplementary table 2. Exploratory clinical outcome for baseline, end of intervention, three-months and one-year.…”

Early mobilisation by head-up tilt with stepping versus standard care after severe traumatic brain injury – Protocol for a randomised clinical feasibility trial

“…Neither the physiological mechanisms causing orthostatic hypotension nor those that enable recovery from this phenomenon have been thoroughly investigated. Considering analysis of electrocardiography (ECG) signals obtained from ABI patients during HUT, we suggested that impairment of baroreceptor sensitivity may be involved [ 8 ]. Whether the impairment is caused by the brain lesion per se or prolonged immobilisation or both remains to be investigated.…”